This Program Project for a Tropical Disease Research Unit proposes study of four parasitic diseases that are endemic in the developing world. Two, leishmaniasis and South American trypanosomiasis, are caused by protoxoa, and filariasis and schistosomiasis are caused by helminths. The present proposal takes an immunologic approach to study of these diseases. Emphasis is placed on delineating and isolating the antigens which induced protective immunity using monoclonal antibodies produced by lymphocyte hybrids. These antigens will be used to develop specific diagnostic tests and eventually vaccines. Studies on the mechanism of protective immunity should aid in the production of the latter, and those on immunpathology should lead to measures to prevent the consequences of infection. In the leishmania project, an emphasis is placed on delineating species specific antigens from organisms prevalent in the New World and on the interaction of different species of leishmania with activated human macrophages. In the filariasis project, in addition to the studies on stage specific antigens and mechanism of immunity and immunopathology, there are studies on the interaction of worms with coagulation factors and platelets. In the trypanosomiasis project, the mechanism of cell-mediated immunity involved in killing blood stream forms of T. cruzi is stressed. In the schistosomiasis projects, emphasis is placed on studying changes on the surface of the schistosomula that lead to immune evasion and those that are caused by immune attack; studies are also proposed on the mechanism of eosinophil-mediated killing of the larvae, and on isolating relevant target antigens. Cores on electron microscopy and morphology, on lymphocyte hybridomas, and on maintaining the life cycles are included.